1. Field of the Invention
The present invention relates to a method for evaluating skin health and an apparatus used therefor.
2. Description of the Related Art
A living body always exchanges a substance and energy with an environment under which the living body exists and it has various functions of adjusting the transport amount or exchange amount of the substance or energy in accordance with an environmental change. Above all, a function of restraining transpiration of water from the skin surface, thereby protecting the living body from drying is called a barrier function and it is medically important. As an index of the barrier function, a water transpiration amount from the skin or a transepidermal water loss (TEWL) has been used widely. In the conventional method, investigation on. a response of the physical properties of the skin to the environment must be carried out while changing the environment in a laboratory. It is utterly unfeasible, because a large-scaled apparatus and much labor and time are required.
The present inventors paid attention to the fact that conventionally, investigation of the TEWL of the skin included only that of the stratum corneum epidermidis but living cells therebelow were not taken into consideration. According to the conventional way of thinking, an increase in TEWL owed to deterioration in the barrier function of the stratum corneum epidermidis. An increase in TEWL, however, is sometimes caused by abnormalities in the living cells below the normal stratum corneum epidermidis, and in such a case, correct diagnosis cannot be conducted.
The present inventors therefore classified the structure of the skin into the stratum corneum epidermidis and living cells therebelow and considered that TEWL might be influenced not only by the water permeability through the stratum corneum epidermidis but also by a difference (driving force) in the activity of water (or water vapor partial pressure) between the structure formed of living cells present below the stratum corneum epidermidis and the outside world. It is presumed that the activity of water in the living cells below the stratum corneum epidermidis reflects the concentration or composition of water and also bio-reaction so that it varies depending on the properties or disease of the skin, metabolism or even age. As described above, the present inventors have found that it is important, for appropriate skin care based on not only the working degree of a barrier function but also the properties or disease of the skin, metabolism or bio-reaction, to evaluate water permeability (overall mass transfer coefficient) through the stratum corneum epidermidis and water supplying capability (activity or water vapor partial pressure) in the living cells below the stratum corneum epidermidis separately from the water transpiration amount measured by using a specified apparatus. The present inventors have also found that the use of these evaluations in combination as an objective index of skin health makes it possible to conduct skin care in accordance with the skin health of each subject.
In one aspect of the present invention, there is thus provided a method for evaluating water permeability through the stratum corneum epidermidis based on a water transpiration amount, which comprises feeding, through a gas inlet, a carrier gas having certain properties to a skin surface to be measured; measuring, by a humidity sensor, the humidity of the carrier gas which has been discharged from a gas exhaust, passing over the skin surface to be measured; and calculating the water transpiration amount from the response of the sensor and calculating, by a predetermined analyzing method, an overall mass transfer coefficient of water in the stratum corneum epidermidis; and an apparatus used for the above-described method.
In another aspect of the present invention, there is also provided a method for evaluating, based on a water transpiration amount, water supplying capability of a structure which lies below the stratum corneum epidermidis and is formed of living cells, which comprises feeding, through a gas inlet, a carrier gas having certain properties to a skin surface to be measured; measuring, by a humidity sensor, the humidity of the carrier gas which has been discharged from a gas exhaust, passing over the skin surface to be measured; and calculating the water transpiration amount from the response of the sensor and calculating, by a predetermined analyzing method, a water vapor partial pressure of the structure which lies below the stratum corneum epidermidis and is formed of living cells; and an apparatus used for the above-described method.
In a further aspect of the present invention, there is also provided a method for evaluating skin health based on a water transpiration amount, which comprises feeding, through a gas inlet, a carrier gas having certain properties to a skin surface to be measured; measuring, by a humidity sensor, the humidity of the carrier gas which has been discharged from a gas exhaust, passing over the skin surface to be measured; and calculating the water transpiration amount based on the response of the sensor and calculating both an overall mass transfer coefficient of water in the stratum corneum epidermidis and a water vapor partial pressure of a structure which lies below the stratum corneum epidermidis and is formed of living cells by employing a predetermined analyzing method.
The terms xe2x80x9cwater permeability through the stratum corneum epidermidisxe2x80x9d, xe2x80x9coverall mass transfer coefficient of the stratum corneum epidermidisxe2x80x9d, xe2x80x9cwater vapor partial pressure of a (the) structure which lies below the stratum corneum epidermidis and is formed of living cellsxe2x80x9d and xe2x80x9cwater supplying capability of a (the) structure which lies below the stratum corneum epidermidis and is formed of living cellsxe2x80x9d may be replaced with the simple terms xe2x80x9cwater permeabilityxe2x80x9d, xe2x80x9coverall mass transfer coefficientxe2x80x9d, xe2x80x9cwater vapor partial pressurexe2x80x9d, and xe2x80x9cwater supplying capabilityxe2x80x9d, respectively.
According to the present invention, it is possible to evaluate water permeability and water supplying capability separately by analyzing the measured value of a water transpiration amount in different manners, and employ them as an index for a barrier function, skin conditions or disease, metabolism or bio-reaction. In addition, it is possible to use them in combination as an objective index of the skin health.